1. Field of the Invention
This invention relates generally to semiconductor processing technology, and, more particularly, to a device and method for contactless metrology.
2. Description of the Related Art
The physical characteristics, and, in particular, the electronic characteristics of the silicon/silicon dioxide (Si/SiO2) interface have played a major role in establishing the dominance of Si in semiconductor technology. As the physical dimensions and critical dimensions (CD) of semiconductor devices such as Complementary Metal Oxide Semiconductor (CMOS) transistors, and the like, continue to shrink, it is becoming increasingly important to understand how thin oxide films influence the charge carrier dynamics at buried Si/SiO2 interfaces. Examples of such influences include charge breakdown and hot carrier injection.
Valence band-offset (Δvb) may be defined as the difference between the top of the valence band 100 in Si and the top of the valence band 105 in SiO2 (see FIG. 1). Similarly, conduction band-offset (Δcb) may be defined as the difference between the bottom of the conduction band 110 in Si and the bottom of the conduction band 115 in SiO2 (see FIG. 1). The band-offsets Δvb and Δcb at the Si/SiO2 interface are important parameters that help determine whether thin oxide films will exert influences such as charge breakdown and hot carrier injection over the charge carrier dynamics. The band-offsets Δvb and Δcb at the Si/SiO2 interface represent barrier heights for carrier injection or quantum mechanical tunneling processes, for example. Bandgap Δbg in Si is about 1.1 eV and bandgap Δbg in SiO2 is about 9 eV (see FIG. 1).
Several techniques have traditionally been used to measure one or more of the band-offsets Δvb and Δcb at semiconductor heterointerfaces (interfaces between different types of materials) such as the Si/SiO2 heterointerface. For example, X-ray photoelectron spectroscopy (XPS) has been employed for measuring valence band-offsets (Δvb). Although this technique allows contactless Δvb measurements, it utilizes X-ray photons of several tens of eVs and is therefore limited in energy resolution to a few hundred meV (a few percent of the X-ray photon energy). Internal photoemission spectroscopy, which can be used for measuring both, the Δvb and conduction band-offsets (Δcb), on the other hand, requires electrical contacts on the device under test to measure the photo-generated current in an external circuit. This becomes increasingly difficult, as gate oxide thicknesses shrink below 40 Å. In addition, for using internal photoemission, the semiconductor has to be doped p-type or n-type to measure Δvb or Δcb, respectively.
The present invention is directed to overcoming, or at least reducing the effects of, one or more of the problems set forth above.